Such over-center float-operated valve actuating mechanisms are useful in controlling the filling of a closed or sealed pressure vessel and in which the vessel includes a vent valve for venting the interior of the vessel to the atmosphere and a second pressure valve subjected to high pressure inlet fluid, such as live steam at 100 to 500 psi, to drive an accumulated liquid periodically from said vessel. In filling such vessel, the vent valve is in the open position and the pressure valve is closed by the single-float operated over-center valve actuating mechanism. As the vessel fills with liquid, the float rises and a rotatable float arm, forming part of the valve actuating mechanism, is swung or rotated about a pivot point at one end thereof remote from the float, causing an over-center toggle linkage mechanism to move toward the center position against a spring bias. Such a mechanism has toggle linkage elements which snap quickly through the center position, closing the vent valve simultaneously with snap opening of the high pressure inlet valve to pump the accumulated liquid from the vessel.
Typically, a tension coil spring provides such biasing force with one end of the coil spring coupled to a fixed or stationary member of the valve mechanism or vessel. In other cases, such tension coil spring is coupled at opposite ends to moveable elements of the valve actuating mechanism.
U.S. patents representative of the state of the art with respect to snap-acting, over-center valve actuating mechanisms particularly useful in periodically filling a vessel with liquid while venting the same and closure of the vent valve upon filling of the liquid to a degree effecting actuation of the over-center valve actuating mechanism and to permit fluid pressure pumping by positive pressure or vacuum pressure of the accumulated liquid from the vessel are the following:
U.S. Pat. No. 1,285,256, issued Nov. 19, 1918, entitled "Liquid Feeding Device" PA0 U.S. Pat. No. 1,406,157, issued Feb. 7, 1922, entitled "Fuel Feeding System for Internal Combustion Engines" PA0 U.S. Pat. No. 1,446,902, issued Feb. 27, 1923, entitled "Vacuum Feeding Device" PA0 U.S. Pat. No. 1,530,218, issued Mar. 17, 1925, entitled "Fluid Supply Apparatus" PA0 U.S. Pat. No. 1,561,159, issued Nov. 10, 1925, entitled "Liquid Level Maintaining Device" PA0 U.S. Pat. No. 1,635,692, issued Jul. 12, 1927, entitled "Valve Snap Action" PA0 U.S. Pat. No. 1,712,985, issued May 14, 1929, entitled "Vacuum Tank" PA0 U.S. Pat. No. 2,172,110, issued Sept. 5, 1939, entitled "Pump" PA0 U.S. Pat. No. 2,394,169, issued Feb. 5, 1946, entitled "Compressed Air Coolant Circulatory Pump" PA0 U.S. Pat. No. 3,242,873, issued Mar. 29, 1966, entitled "Automatic Bilge Pump"
While such over-center snap-acting valve mechanisms for steam condensate pumps and fuel feeding systems operate satisfactorily to automatically control the liquid feed to and discharge from the pressure vessels, such known mechanisms are complex and expensive, fail to ensure maintaining the two alternately openable and closable valves in full, high-pressure biased, closed condition when closed, or fully open, when open. Particularly, the snap-acting movable valve mechanisms tend to move prior to the over-center toggle linkage mechanisms reaching the center line position where snap action, multi-valve state reversal occurs.
It is, therefore, a primary object of the present invention to provide an improved snap-acting, over-center valve actuating mechanism particularly useful for simultaneous actuation and alternating reversal of a normally open valve and a normally closed valve which alternately open and close in both directions of movement of a snap over, toggle linkage, wherein the mechanism is of low cost, of simplified construction, and which preferably employs a relatively short axial length, stiff compression coil spring having a large spring constant and being subject to spring preloading, and in which the compressive biasing force of the spring is maintained at all times to ensure that the normally closed valve remains closed under a high-biasing force, and the normally open valve remains open, and with movement of the toggle linkage mechanism limited to low friction pivoting of the coil spring about both ends thereof, as one of two toggle links, until the toggle linkage reaches the center line position at which point the toggle linkage rapidly snaps across the mechanism center line.